The present invention relates to manufacturing methods and apparatuses of an optical device and a reflection plate, that include a resin thin film having a micro-asperity pattern.
In this specification, xe2x80x9cmicro-asperity patternxe2x80x9d is a generic term of asperity shapes that develop one-dimensionally or two-dimensionally and are 0.1 xcexcm to hundreds of micrometers in depth and arbitrary in width, length and shape.
xe2x80x9cReflection-type liquid crystal display devicexe2x80x9d is a generic term of devices in which a liquid crystal is sealed between a transparent counter substrate having a transparent electrode and an active matrix substrate having a reflection surface that is provided with a surface micro-asperity pattern.
Nowadays, liquid crystal display devices are increasingly applied to personal computers, TV receivers, word processors and video equipment, etc. On the other hand, to increase the functionality and reduce the size, power consumption, cost, etc. of such electronic equipment, reflection-type liquid crystal display devices that display an image by reflecting external light instead of using a backlight are being developed.
FIG. 17 shows an example of such reflection-type liquid crystal display devices. A reflection plate 1 used in the reflection-type liquid crystal display device is disposed under a counter substrate 28 that is composed of a transparent electrode facing a liquid crystal layer 27, a color filter layer formed over the transparent electrode, a surface glass substrate disposed over the color filter layer, and other members. The reflection plate 1 is used to increase the viewing angle of the image display of the liquid crystal display device by diffuse-reflecting light coming from the counter substrate 28.
The reflection plate used in this liquid crystal display device is formed by a melting method in which a photosensitive resin material is coated by spin coating or the like on the surface of a substrate made of glass or resin or the surface of a substrate in which TFT transistors, liquid crystal driving elements, etc. are formed on such a substrate and is patterned through photolithography to form an asperity pattern whose cross section has an almost rectangular shape. A smooth curved surface is then formed by surface tension through heat treatment.
An embossment, in which a micro-asperity pattern stamper is pressed against a resin thin film coated on a substrate, whereby a micro-asperity pattern is formed, is also known.
In the reflection-type liquid crystal display device, as shown in FIG. 18, a thin film transistor or a wiring contact 31 is disposed under a resin thin film 4 having a micro-asperity pattern 40. Thus, a contact hole 37 penetrating the resin thin film 4 needs to be formed in order to obtain electrical contact.
In case where the micro-asperity pattern 40 is formed through the conventional melting method, the contact hole is made through photolithography using a photosensitive resin. This photolithography technique is suitable for forming the contact hole because it can make a through-hole without damaging a layer disposed therebelow as does wet etching using a strong acid or alkali solution or dry etching using reactive plasma does.
However, the melting method has problems that 1) three-dimensional degree of freedom that realizes an acute-angled or plane shape is low because the method makes an application of shape sagging, 2) a shape varies with a variation in melting conditions thus resulting in low processing accuracy, and 3) a large number of processing steps increases cycle time.
On the other hand, the embossment method has a high degree of three-dimensional freedom since a stamper transfers a micro-asperity pattern to the resin thin film. And this method can attain a micro-asperity pattern with high reproducibility. Furthermore, the embossment method can use any resin material if it is melted, leaving a wide range of choices.
However, the embossment method cannot maintain photosensitivity of a photosensitive resin thin film after a micro-asperity pattern of the resin thin film is formed when the photosensitive resin thin film is spin-coated on the surface of a substrate and heated to an appropriate temperature for press-shaping the resin thin film by using a stamper. This results in extinction of the photosensitivity.
The present invention provides a manufacturing method and apparatus of an optical device having a micro-asperity pattern, which are able to form various kinds of three-dimensional shapes with satisfactory processing accuracy and realize them as thin films.
The invention further provides manufacturing methods and apparatuses of an optical device and a reflection plate, each of which has liquid crystal driving elements or wiring contacts that are disposed under a micro-asperity pattern and has a conducting passage leading from a reflection plate placed on the top surface of the micro-asperity pattern to the liquid crystal driving elements or the wiring contacts.
The invention provides a manufacturing method of an optical comprising: coating a substrate 5 with a resin thin film 4 made of a photosensitive resin; controlling a temperature of the resin thin film 4 to a temperature that is lower than the photosensitivity extinction temperature so as to soften or melt the resin thin film 4; and pressing a die having an inverted micro-asperity pattern against the resin thin film 4 in a state that the resin thin film 4 has been softened or melted, whereby a micro-asperity pattern is formed on a surface of the resin thin film 4.
In this manufacturing method, the die has a member or portion having an inverted shape of that of at least a micro-asperity pattern to be formed on the surface of a resin thin film, and may be either a press male die or a roller-type die.
The optical device means an element whose surface is formed with at least a micro-asperity pattern to perform diffusion, focusing and reflection of light.
In this manufacturing method, the micro-asperity pattern surface of the die is pressed against the resin thin film, whereby a micro-asperity pattern is formed on the surface of the resin thin film. Therefore, the micro-asperity pattern that is left on the resin thin film is given an arbitrary three-dimensional shape. That is, a micro-asperity pattern can be obtained with a high degree of freedom and high reproducibility.
Since the temperature of the resin thin film formed on the substrate is controlled to a temperature that is lower than the photosensitivity extinction temperature of the resin thin film, it is possible to form a through-hole in the resin thin film or easily cut the shape of the resin thin film into an appropriate shape by photolithography, if required, after the temperature is controlled.
The micro-asperity pattern can be laid out regularly or arbitrarily by executing the die pressing step a number of times on the resin thin film.
In the invention, it is an effective measure to make adjustments by causing a relative movement between the substrate and the die so that a substrate-side alignment mark provided on the substrate coincides with a reference position on the die side. Using this technical measure, an error in the position of the substrate with respect to the die can be corrected by causing a relative movement between the substrate and the die so that the substrate-side alignment mark provided on the substrate coincides with the reference position on the die side. As a result, a micro-asperity pattern can be formed with high processing accuracy.
In the invention, it is also an effective measure to form a micro-asperity pattern on the surface of the resin thin film at an inert gas atmosphere or a low-pressure atmosphere having a pressure that is lower than atmospheric pressure. Using this technical measure, the air is exhausted in advance from a chamber that accommodates the manufacturing device for manufacturing an optical device. Therefore, oxygen and impurities contained in the air inside the chamber are exhausted and a micro-asperity pattern can be formed in a clean, inert gas atmosphere. This makes it possible to not only prevent the resin thin film from being oxidized or changed in quality but also prevent the phenomenon where impurities stick to the resin thin film during formation of a micro-asperity pattern and are finally fixed to the micro-asperity pattern formed, whereby the production yield of the optical device can be increased.
Particularly, when the pressure inside the chamber is lowered, air is no longer trapped between the die and the resin thin film and a micro-asperity pattern that is free of air bubbles can be formed. If air bubbles existed, they would act as a damper and hence necessitate stronger pressing force. Without air bubbles, the pressing force can be made weaker, as a result of which residual stress in a micro-asperity pattern formed decreases. Therefore, the production yield of the optical device can be increased.
The resin thin film may be of a polyimide (PI) type or acryl type. Polyimide (PI) has thermoplasticity. It is desirable that the polyimide-type resin be fully aromatic polyimide such as polyetherimide (PEI) or polyamideimide (PAI).
In case of the PI-type resin and acryl-type resin, the photosensitivity extinction temperature is about 100-150xc2x0 C. The temperature of the resin thin film when it is pressed is set lower than the photosensitivity extinction temperature. Since the photosensitivity is varied as a heating temperature of the heating means is changed, it is desirable that the press temperature be set at photosensitivity extinction temperature minus 10xc2x0 C.
According to another aspect of the invention, there is provided a manufacturing apparatus of an optical device, comprising a transfer stage disposed under a die having an inverted micro-asperity pattern, for holding a substrate that is coated with a resin thin film; a transfer stage transfer direction moving mechanism for reciprocating the transfer stage between an initial position and a movement end position where a movement that starts from the initial position ends; and a pressurizing mechanism for pressing the die against the resin thin film at a prescribed position, wherein a micro-asperity pattern is formed on a surface of the resin thin film by pressing the die against the resin thin film with the pressurizing mechanism.
The transfer stage transfer direction moving mechanism is a mechanism for moving the transfer stage that holds the substrate rightward from the initial position to the movement end position (it is assumed that the initial position is located on the left side) while a micro-asperity pattern is formed on the resin thin film, and for returning the transfer stage from the movement end position to the initial position. As mentioned above, the die may be either a press male die or a roller-type die.
In this manufacturing apparatus, the die is pressed against the resin thin film while the substrate on the transfer stage is moved from the initial position to the movement end position, whereby a micro-asperity pattern is formed. Therefore, an optical device having a micro-asperity pattern that has been formed with high processing accuracy can be provided.
The invention also provides a manufacturing apparatus of an optical device, comprising a transfer stage disposed under a die having an inverted micro-asperity pattern, for holding a substrate that is coated with a resin thin film; a pressurizing mechanism for pressing the die against the resin thin film at a prescribed position; and a pressurizing mechanism transfer direction moving mechanism for reciprocating the pressurizing mechanism between an initial position and a movement end position where a movement that starts from the initial position ends, wherein a micro-asperity pattern is formed on a surface of the resin thin film by pressing the die against the resin thin film with the pressurizing mechanism.
The pressurizing mechanism transfer direction moving mechanism is a mechanism for moving the pressurizing mechanism on the resin thin film rightward from the initial position to the movement end position (it is assumed that the initial position is located on the left side), while a micro-asperity pattern is formed on the resin thin film, and for returning the pressurizing mechanism from the movement end position to the initial position. As mentioned above, the die may be either a press male die or a roller-type die.
In this manufacturing apparatus, the die is pressed against the resin thin film while the pressurizing mechanism is moved from the initial position to the movement end position, whereby a micro-asperity pattern is formed. Therefore, an optical device having a micro-asperity pattern that has been formed with high processing accuracy is provided.
It is desirable that the apparatus be configured in such a manner that the substrate is disposed under the die so as to be able to move in an X-direction and a Y-direction and rotate about a Z-axis that points to the die, whereby a position of the substrate can be adjusted with respect to the die. Using this technical measure, since the substrate can be moved in the X-axis and the Y-axis with respect to the die and can be rotated about the Z-axis, the position of the substrate with respect to the die can be adjusted. Therefore, an optical device that has been manufactured with high processing accuracy can be provided.
In the invention, it is an effective measure to give the die a cylindrical shape in which the outer circumferential surface is formed with the inverted micro-asperity pattern, and to form a micro-asperity pattern on the surface of the resin thin film as the die rolls on the surface of the resin thin film 4 while being pressed against the resin thin film.
With this technical measure, a micro-asperity pattern is formed as the cylindrical die whose outer circumferential surface is formed with the inverted micro-asperity pattern is pressed against the resin thin film. Therefore, even if air bubbles exist inside the resin thin film, they are pushed and moved by the recesses of the inverted micro-asperity pattern of the die in the direction opposite to the movement direction of the resin thin film (in the case where the resin thin film is moving) or the movement direction of the die (in the case where the die is moving) and are broken by the projections of inverted micro-asperity pattern, whereupon the air goes out of the resin thin film. This reduces the probability of a phenomenon where a micro-asperity pattern produced is deformed by air bubbles that remain inside the resin thin film, and as a result, the yield is increased.
In the invention, it is an effective measure to employ a transfer stage crossing direction moving mechanism for moving the transfer stage in a crossing direction that crosses a micro-asperity pattern transfer direction, whereby a relative movement can be caused between the resin thin film and the die in both the micro-asperity pattern transfer direction and the crossing direction.
A micro-asperity pattern is transferred to the resin thin film by means of the die. If the position of the substrate that is provided on the transfer stage is deviated from the reference position of the die, a micro-asperity pattern is not formed at a prescribed position. It is therefore necessary to move the transfer stage perpendicularly to the die movement direction. The transfer stage crossing direction moving mechanism is provided for this purpose. Although it is desirable to move the transfer stage completely perpendicularly to the micro-asperity pattern transfer direction, high-level techniques are needed to do so because of manufacturing errors. The transfer stage need not always be moved completely perpendicular to the micro-asperity pattern transfer direction.
Using this technical measure, the initial position of the substrate that is held by the transfer stage can be adjusted by causing a relative movement between the transfer stage and the die in the micro-asperity pattern transfer direction and the crossing direction by using the transfer stage crossing direction moving mechanism and the transfer stage transfer direction moving mechanism for reciprocating the transfer stage between the initial position and the movement end position or the pressurizing mechanism transfer direction moving mechanism for reciprocating the pressurizing mechanism between the initial position and the movement end position. Another mode of operation is possible that after a first micro-asperity pattern is formed by the die, the transfer stage is moved by the transfer stage crossing direction moving mechanism and a second micro-asperity pattern is formed beside the first one.
In the invention, it is an effective measure that the die comprise a stamper to be pressed against the resin thin film to form a micro-asperity pattern on its surface, a base for holding the stamper, and an elastic member interposed between the stamper and the base.
With this technical measure, the elastic member absorbs manufacturing errors such as undulation in the stamper and the base, whereby the micro-asperity pattern processing accuracy can be increased.
It is also effective that the die comprise a stamper to be pressed against the resin thin film to form a micro-asperity pattern on its surface, a roll body for holding rotatably the stamper, and an elastic member interposed between the stamper and the roll body.
Using this technical measure, the elastic member absorbs manufacturing errors such as undulation in the stamper and the roll body, whereby micro-asperity pattern processing accuracy can be increased.
In the invention, it is effective that the apparatus have heating units for heating the die and the transfer stage, and a temperature controller for controlling the heating units. Using this technical measure, the cycle time of a manufacturing process can be made constant and an optical device having a micro-asperity pattern that has been formed with high processing accuracy can be provided.
In the invention, it is effective that the pressurizing mechanism comprise at least one alignment mark observation optical device so that at least one alignment mark provided on the substrate can be recognized visually. It is also an effective measure to employ at least one alignment mark observation optical device that is disposed under the substrate so that at least one pair of a first alignment mark provided on the substrate and a second alignment mark provided on the die can be recognized visually. As long as the alignment mark observation optical device is disposed under the substrate, it may be provided inside the transfer stage or the above-mentioned rotation moving mechanism or may bridge the transfer stage and the rotation moving mechanism. This technical measure makes it possible to form a micro-asperity pattern having high position accuracy.
The invention also provides a manufacturing apparatus of an optical device, comprising a transfer stage for holding a substrate that is coated with a resin thin film; a pressuring mechanism for pressing a die having an inverted micro-asperity pattern against the resin thin film at a prescribed position; a moving mechanism for moving one of the transfer stage and the die while the die is pressed against the resin thin film; and an airtight chamber having an exhaust mechanism, the airtight chamber accommodating the transfer stage, the die, the pressurizing mechanism, and the moving mechanism, wherein the exhaust mechanism exhausts a gas from the airtight chamber prior to an operation that a micro-asperity pattern is formed on a surface of the resin thin film by pressing the die against the resin thin film.
In this manufacturing apparatus, the exhaust mechanism for exhausting a gas from the airtight chamber is used prior to an operation that a micro-asperity pattern is formed on the surface of the resin thin film by pressing the die against the resin thin film. Therefore, oxygen and impurities contained in the air inside the airtight chamber are exhausted and a micro-asperity pattern can be formed in a clean, inert gas atmosphere. This makes it possible to not only prevent the resin thin film from being oxidized or changed in quality but also prevent a phenomenon that impurities stick to the resin thin film during formation of a micro-asperity pattern and are finally fixed to the micro-asperity pattern formed, whereby the production yield of an optical device can be increased.
According to another aspect of the invention, there is provided a manufacturing method of an optical device, comprising the steps of coating a substrate with a photosensitive resin thin film; controlling a temperature of the resin thin film to a temperature that is lower than the photosensitivity extinction temperature of the resin thin film, so as to soften or melt the resin thin film; pressing a die having an inverted micro-asperity pattern against the resin thin film in a state that the resin thin film has been softened or melted, whereby the micro-asperity pattern is formed on a surface of the resin thin film; forming a through-hole leading from the surface of the micro-asperity pattern to the surface of the substrate by photolithography; and sintering the resin thin film at a temperature that is higher than the photosensitivity extinction temperature of the resin thin film.
In this manufacturing method, the micro-asperity pattern surface of the die is pressed against the resin thin film, whereby a micro-asperity pattern is formed on the surface of the resin thin film. Therefore, the micro-asperity pattern that is left on the resin thin film is given an arbitrary three-dimensional shape. That is, a micro-asperity pattern can be obtained with a high degree of freedom and high reproducibility.
Since the temperature of the resin thin film coated on the substrate is controlled to a temperature lower than the photosensitivity extinction of the resin thin film, a through-hole can be easily formed when it is opened in the resin thin film by photolithography.
Although a sintering temperature is set higher than the photosensitivity extinction temperature, it is desirable that the sintering temperature be set higher than 200xc2x0 C. in order to avoid generation of gas caused by decomposition of a volatile remaining photosensitive component of a residual solvent in the resin thin film. Therefore, an alignment film made of polyimide resin can be sintered at 200xc2x0 C. after the micro-asperity pattern of the resin thin film is formed.
It is also desirable that the glass transition temperature of the photosensitive resin be at least 200xc2x0 C. after sintering in order to prevent the micro-asperity pattern from losing its shape during the sintering.
The invention also provides a manufacturing method of a reflection plate, comprising the steps of coating a substrate on which thin-film liquid crystal driving elements or wiring contacts are formed with a photosensitive resin thin film; controlling a temperature of the resin thin film to a temperature that is lower than the photosensitivity extinction temperature of the resin thin film, so as to soften or melt the resin thin film; pressing a die having an inverted micro-asperity pattern against the resin thin film in a state that the resin thin film has been softened or melted, whereby the micro-asperity pattern is formed on a surface of the resin thin film; forming a through-hole leading from the surface of the micro-asperity pattern to the thin-film liquid crystal driving elements or wiring contacts by photolithography; forming a reflection film on the inner surface of the through-hole and the surface of the micro-asperity pattern; and sintering the resin thin film at a temperature that is higher than the photosensitivity extinction temperature of the resin thin film.
In this manufacturing method, the photosensitive resin thin film is formed on the substrate on which the thin-film liquid crystal driving devices or wiring contacts are formed in advance and the temperature of the resin thin film is controlled so as to be lower than the photosensitivity extinction temperature, whereby the micro-asperity pattern is press-formed on the resin thin film by the die in a state that the resin thin film has been melted. Therefore, the resin thin film does not lose its photosensitivity caused by photolithography.
In this manufacturing method, the through-hole is formed from the micro-asperity pattern surface to the thin-film liquid crystal driving device or wiring contact, the reflection film made of a metal material is formed on the micro-asperity pattern surface including the inner surface of the through-hole, and then the resin thin film is sintered at a temperature higher than the photosensitivity extinction temperature. Accordingly, the micro-asperity pattern is not subjected to high-temperature sintering before the reflection film is formed. Therefore, the reflection plate having the micro-asperity pattern can be easily manufactured without losing the photosensitivity of the resin thin film.